8.1 Identifying DNA as the Genetic Material

Open books to page 234. In your notebooks read about histograms and answer question 1 and 2.

8.1 Identifying DNA as the Genetic Material

KEY CONCEPT DNA was identified as the genetic material through a series of experiments.

8.1 Identifying DNA as the Genetic Material

Frederick Griffith 1928 finds a ‘transforming principle.’

• Griffith experimented with the bacteria that cause pneumonia.

• He used two forms: the S form (deadly) and the R form (not deadly).

• A transforming material passed from dead S bacteria to live R bacteria, making them deadly.

8.1 Identifying DNA as the Genetic Material

Charles Avery, 1944, identified DNA as the transforming principle. • Avery isolated and purified Griffith’s transforming

principle.• Avery performed three tests on the transforming

principle.– Qualitative tests showed DNA was present.– Chemical tests showed

the chemical makeupmatched that of DNA.

– Enzyme tests showedonly DNA-degradingenzymes stoppedtransformation.

8.1 Identifying DNA as the Genetic Material

Hershey and Chase,1952, confirm that DNA is the genetic material.

• Hershey and Chase studied viruses that infect bacteria, or bacteriophages.

• Tagged DNA was found inside the bacteria; tagged proteins were not.

– They tagged viral DNA with radioactive phosphorus.– They tagged viral proteins with radioactive sulfur.